Nvidia Geforce 7800GT OC --- Stability Problems

I have a Gateway 835GM with 1024mb of memory, Pentium D 820, and a 7800GT OC. Just recently, I have been having problems with the screen glitching out while playing any kind of game. It's usually fine just cruising the internet and watching videos, but as soon as I start up any video game I am lucky if I can play for 2 minutes before I have to restart. This is what I have tried and checked in my diagnosis:

- Monitored temperature to ensure that it was not overheating, it didnt get above 75 or 80 degrees fahrenheit. Just to make sure, I re-seated the card and cleaned the heatsink with compressed air.
- Underclocked both the core clock and memory frequencies to 75%, 50%, and 25% power and I was still crashing.

I have a Gateway 835GM with 1024mb of memory, Pentium D 820, and a 7800GT OC. Just recently, I have been having problems with the screen glitching out while playing any kind of game. It's usually fine just cruising the internet and watching videos, but as soon as I start up any video game I am lucky if I can play for 2 minutes before I have to restart. This is what I have tried and checked in my diagnosis:

- Monitored temperature to ensure that it was not overheating, it didnt get above 75 or 80 degrees fahrenheit. Just to make sure, I re-seated the card and cleaned the heatsink with compressed air.
- Underclocked both the core clock and memory frequencies to 75%, 50%, and 25% power and I was still crashing.

I reseated the card yesterday and played WoW on it all night and some of today, when it crashed again. If this helps anyone, it seems to last a good ammount of time when it is reseated or played with inside the case. Maybe the power connector is messed up?

I did some more work today. I figured out that the card is perfectly stable if the auxiliary power cable is not plugged into the card. Does this mean that the power supply is not performing up to par to run the graphics card when it it plugged in and running fully?